1. Field of the Invention
The present invention relates to a process for production of a composition which may be used to prepare animal feed.
2. Discussion of the Background
Tryptophan and threonine (Trp and Thr, respectively, herein) are essential amino acids for animals which may be produced by chemical or biochemical processes.
As one of the biochemical processes which may be used to produce these amino acids, a process is known wherein a microorganism having an ability to produce tryptophan or threonine is cultured with sugars, etc. as the main carbon source and ammonia, etc. as the main nitrogen source so as to produce Trp or Thr. Trp or Thr is isolated from the culture liquor and then subjected to crystallization to isolate Trp or Thr in crystal form, the crystals are dried on a conical drier, a fluidized drier, etc. and used in animal feed.
While the prior art has recognized that Trp or Thr may be added to an animal feed in a purified form, there has been no report regarding a process in which a solution containing large amounts of impurities is directly dried without isolating and purifying Trp or Thr to produce a composition for animal feed.
Although the addition Trp or Thr in a crude form which is not isolated and purified, may be considered to be desirable since the composition to which Trp or Thr is to be added is itself extremely vaguely defined, and even when Trp or Thr are added in conjunction with impurities such as sugars, salts, organic acids, etc., these amino acids can still exhibit their nutritional characteristics in a similar fashion to the isolated and purified ones, there are a number of problems associated with preparation of a composition from impure Trp or Thr. When an impure solution of Trp or Thr is dried by a conventional spray drier, the impurities being microscopic ones such as sugars, salts, organic acids, etc., a large amount of the Trp or Thr and other materials become stuck to the apparatus wall or to a separating cyclone. Thus, normal drying cannot be effected under these conditions. When impure Trp or Thr is dried in a drum drier, decomposition due to heat degeneration takes place. Further, since the water content in the product is increased, stability is lowered and other problems occur such as poor miscibility with animal feeds, based on the physical properties of the powder, such as cohesiveness, etc. On the other hand, although there exist other drying means which might be compatible with impure solutions of Trp or Thr such as freeze-drying, vacuum drying, etc., and which are capable of reducing heat degeneration, there is still an economical problem since the production cost using these methods is quite high.
Therefore, a method has been sought for producing a composition for animal feed by drying a Trp or Thr solution, which can produce a product having excellent stability and powder physical characteristics, with minimum decomposition due to heat degeneration and at a low cost. Thus, there remains a need for new methods of preparing compositions for animal feed based on drying a solution of Trp or Thr containing impurities.